In recent years, progress of electrical equipment such as portable information terminal equipment including mobile phones, computers and peripheral equipment thereof, various information home appliances, etc. is remarkable, and high functionality, size reduction, and increase in speed are rapidly advanced.
Following this, in circuit boards to be mounted on such electrical equipment, densification of circuits is more and more required. In order to realize such densification of circuit boards, a method for precisely forming a circuit having narrower line width and line spacing (width of a portion between an electrical circuit and an electrical circuit adjacent to each other) is demanded.
In densified wirings, a short circuit or migration between the wirings is easily generated. In addition, with an increase of the lamination number, irregularities generated on a circuit forming plane become large, and fine circuit formation becomes more difficult.
As a fine circuit formation technique, techniques adopting a subtractive process, an additive process, or the like, which are conventional circuit forming methods of printed wiring boards, are known. In addition, in recent years, a novel fine circuit formation technique with using a laser light is proposed (Patent Document 1).
In a conventional circuit formation step of a printed wiring board, a resist material is used, and the resist material is similarly used in the circuit formation step of Patent Document 1.
However, a film thickness of the resist material which is used in Patent Document 1 is thin as from about 1 to 2 μm, so that it is not easy to form a resist coating having a uniform film thickness at the time of actual production. In addition, in general, even in a dry film resist (DFR) which is used as a technique for forming a uniform film, if the film thickness is too thin, there is a concern that it is lacking in reliability from the standpoint of uniformity.
For that reason, if the film thickness of the resist material can be made thick, such is more preferable from the standpoint of production. However, if the film thickness of the resist material is made thick, laser processability or developability is lowered, or there is caused such a problem that precision of a circuit which is formed by means of mechanical processing is lowered, or the like.
For that reason, a resist material in which even if the film thickness of the resist material is made thick, laser processability, developability, and the like are not affected is desired.
Regarding this issue, Patent Document 2 proposes a resin composition in which for the purpose of enhancing laser processability of a resin, an ultraviolet absorber and the like are blended in a thermosetting resin.
However, in the resin composition of Patent Document 2, since a softening temperature of the resin is too high, there is such a problem that after laser processing, the resin composition is cracked, so that a resist performance, namely resistance to plating chemicals, alkali developability, plating formability, and the like are impaired. Thus, it is the actual situation that a resin composition having both laser processability and resist performance is not obtained yet.